1. Technical Field
The present invention relates to a lamp structure and more particularly to a lamp structure which is applicable to an adaptive streetlight and which has a surface-structured diffusion plate in order to provide a particular light pattern that matches the curvature of the road section to be illuminated.
2. Description of Related Art
Nowadays, with the expansion of transportation networks, the quality of road lighting determines to a large extent whether the roads being illuminated are safe. Road lighting, therefore, plays an important role in the safety of life and property of all road users.
The conventional streetlights, be they equipped with the traditional light bulbs or the more energy-saving LEDs, cannot change their light patterns according to road curvatures. While the resulting problem of insufficient lighting can be solved by installing more streetlights, a significant increase in cost and energy consumption ensues.
FIG. 7A is a schematic top view of a road illuminated by a plurality of conventional streetlights 500 or commercially available streetlights. Typically, the light pattern 510 of the light projected on the ground by a conventional streetlight 500 is localized and lies only around the streetlight such that the road surface is poorly lit. Aside from an uneven distribution of illuminance over the road surface, part of the optical energy is cast outside the road. If the road has a steep slope, the light may even strike the road users' eyes, which causes glare and a considerable waste of energy.
To achieve the road surface illuminance required by law, it is common practice to increase the working power or number of the conventional streetlights 500, leading, however, to excessive power consumption or a wasteful use of resources.
Moreover, some conventional streetlights 500 or commercially available streetlights have a conventional diffusion plate, which is generally made by incorporating micro particles into a substrate, coating a substrate with micro particles, or providing a substrate with a diffusive surface structure.
Mixing micro particles into a substrate does increase diffusivity effectively but reduces permeability of light. Coating a substrate with micro particles tends to have a low yield, and the coated substrate is prone to damage and diffuses light in directions that cannot be controlled.
A diffusive surface structure, on the other hand, is typically made by grinding a substrate's surface with micro particles so that the surface has an irregular roughened texture. A notable example of products with a diffusive surface structure is ground glass. While such surface structures are diffusive to a certain degree, the directions of light diffusion remain uncontrollable.
In view of the above, it is an important issue for the lighting industry or even the entire transportation industry to overcome the aforesaid drawbacks of the conventional streetlights 500 and to provide a lamp structure which meets the requirements of highly uniform light distribution, high diffusivity, and high permeability of light, and which therefore contributes to enhancing the quality of life of the general public. To this end, it is most desirable that a highly efficient refractive optical element (ROE), or more particularly a surface-structured diffusion plate, can be made by forming a micro lens array (i.e., surface structure) on the surface of a substrate.